This invention relates generally to switches for optical networks and in particular to dynamically reconfigurable switching systems for optical telecommunications networks.
As optical fiber progressively supplements and replaces metal wire as the backbone of telecommunications networks, the switches that route optical signals have emerged as a significant bottleneck. Transmission systems move information as optical photons but the switching systems and so-called crossconnect fabrics that switch, route, multiplex, and demultiplex optical signals have generally been electronic. Electronic switching requires light to be converted to an electronic signal to pass through the switch and then be reconverted to light in a process termed optical-electronic-optical (OEO) conversion that introduces both time delay and cost.
There is great interest in the telecommunications industry, therefore, in developing all optical switching to avoid the necessity of multiple OEO conversions. On long haul networks, ten""s or hundred""s of individual wavelengths, each carrying a signal, are multiplexed onto each fiber. Switches are desired that provide all optical switching at the fiber level, the wavelength level, or at both levels. As described, for example, by Bishop et al. in Scientific American (January, 2001, pp 88-94), all optical switches based on a number of underlying technologies including Micro Electro Mechanical Systems (MEMS) tilting mirrors, thermo-optical devices, bubbles formed by inkjet printing heads, and liquid crystals, have been proposed.
Optical crossconnect systems using these underlying optical switching technologies have been classified by Telcordia Technologies. All of the crossconnect systems have at their core a device, frequently termed a switching fabric, having multiple input ports and multiple output ports. In general, the switching fabric allows a signal from any input port to be coupled to any output port. According to the standard Telcordia definitions, fiber crossconnect (FXC) systems link external connectors directly to specific ports of a switching fabric. Wavelength selective crossconnect (WSXC) systems include, in addition, wavelength demultiplexers and multiplexers. In WSXC systems the input fibers are connected to wavelength demultiplexers. The outputs of the demultiplexers are linked to specific input ports of a switching fabric. Specific output ports of the switching fabric are linked to inputs of wavelength multiplexers and outputs of the multiplexers are linked directly to external output connectors. Wavelength interexchanging crossconnect (WIXC) systems are similar to WSXC systems with the addition of wavelength converters between the output of the switching fabric and the wavelength multiplexers. Finally, the Telcordia classification scheme includes the term hybrid optical crossconnect systems to describe combinations of FXC, WSXC, and WIXC systems.
One example of a WIXC or hybrid system is described in U.S. Pat. No. 5,694,499 to Tillerot et al. which discloses an optical crossconnect system including provisions for demultiplexing multiple signals, optically filtering and wavelength converting the signal, and multiplexing the outgoing signals. However, in the system of Tillerot et al. as well as in the crossconnect systems described by the standard definitions, the optical paths between input signals and output signals are generally rigid, that is the connections between the different optical components are fixed.
Optical switching systems that are not limited to predetermined connections while limiting OEO conversions would further the development of fiber optic telecommunications networks.
A dynamically reconfigurable optical switching system serves as a node on a fiber optic telecommunication network. The optical switching node according to embodiments of the present invention utilizes an optical switching fabric, a switching device with multiple input ports and multiple output ports that can be controlled to direct a signal from a particular input port to a particular output port.
An input port of at least one demultiplexer is optically connected to an output port of the switching fabric and the multiple output ports of the demultiplexer, for transmitting single-wavelength signals, are each optically connected to an input port of the switching fabric. The multiple input ports of at least one multiplexer, for receiving single wavelength signals, are each optically connected to an output port of the switching fabric and the output port of the multiplexer, for transmitting a multi-wavelength signal, is optically connected to an input port of the switching fabric.
The optical switching node also includes an external fiber connector with connections for receiving a multi-wavelength signal from the network and connections for transmitting a multi-wavelength signal to the network, and a switching node controller. The switching node controller is connected to a management infrastructure of the optical network via a digital electronic connection or a dedicated optical channel. The switching node controller also is connected to provide instructions to the optical switching fabric to direct a signal from a particular input port to a particular output port. The optical switching node may also include optical signal conditioners such as optical amplifiers, wavelength converters, and optical signal correctors that modify optical signals. Output ports of the switching fabric are optically connected to input ports of the optical signal conditioners and output ports of the optical signal conditioners are optically connected to input ports of the switching fabric. The system architecture of the present optical switching node allows an incoming optical signal to be directed through any desired combination of optical components via multiple traversals of the switching fabric.
In other embodiments, the optical switching node includes one or more fixed configuration wavelength demultiplexers having an input port optically connected to the external fiber connector for receiving incoming multi-wavelength signals and multiple output ports directly connected to input ports of the switching fabric. In addition, the optical switching node may include one or more fixed configuration wavelength multiplexers having an output port optically connected to the external fiber connector for transmitting multi-wavelength signals to the network and multiple input ports optically connected to output ports of the switching fabric. Use of the fixed configuration demultiplexers and multiplexers enables signals to be processed with fewer traversals of the switching fabric. According to yet another embodiment, a connector in the external fiber connector for receiving single wavelength signals is optically connected to an input port of the switching fabric and a connector in the external fiber connector for transmitting single wavelength signals is optically connected to an output port of the switching fabric. The single wavelength connectors in the external fiber connector allow the optical switching node to serve as an add/drop multiplexer.
The optical switching node may also include a signal splitter that divides an optical signal into a large amplitude portion and a small amplitude portion and directs the small amplitude portion via the switching fabric to a performance monitoring module. The performance monitoring module is electrically connected to the switching node controller which may send instructions to the fabric controller to control the switching fabric based on the performance information. The optical switching node may also include a signaling access module for separating signaling information embedded in data carried on a single-wavelength of a multi-wavelength signal. The signaling access module is optically connected to the switching fabric and electrically connected to the switching node control.
In some embodiments, the present optical switching node is a configurable optical add/drop multiplexer at a network node of, for example, a ring network. The configurable add/drop multiplexer, based on an optical switching fabric, includes connections for transmitting and receiving multi-wavelength network signals and for transmitting and receiving single-wavelength local add/drop signals. The configurable add/drop multiplexer further includes multiplexers, demultiplexers, and a switching node controller, and may also include one or more optical amplifiers and/or wavelength converters and a performance monitoring module.
Methods of using the optical switching node to process optical signals are also provided.